The numerous forces and stresses imparted to both the interior and exterior components of a space craft by its launch vehicle must be load-pathed carefully throughout the structure to preclude damaging the payload components carried by the spacecraft. These payload components often may be of more delicate construction than either the launch vehicle or the spacecraft itself. The space shuttle as a launch vehicle imposes a variety of primarily transverse and random forces on its payload, whereas expendable launch vehicles impose primarily longitudinal and random forces on the spacecrafts to which they are detachably connected.
In the past, load-paths have been provided through the components within the spacecraft by a system of "launch locks" which temporarily connect these components together via a plurality of metal shafts and interconnected pieces which must later be disconnected so as to move with respect to each other. After the stresses of a launch are over, the metal shafts of the "launch-locks" must be severed mechanically to permit the previously connected spacecraft components to move relative to each other as required for accomplishment of the tasks for which designed. Prior art techniques for disengaging the shaft of the launch locks may prove unreliable because they involve severing a relatively heavy metal bolt with a relatively heavy bolt cutter. These prior art bolt cutting devices are relatively complicated and heavy because the bolt cutting assembly generally includes a bolt catcher and a pyrotechnic actuator for driving a single or redundant cutter through a metal shaft of relatively large diameter. Due to variations in the shear resistance of the metal shaft and the driving force of the pyrotechnical device, the bolt cutter may fail to sever the metal shaft of the launch lock, leaving connected component parts of the spacecraft that need to be freed for relative movement in order to properly carry out the mission of the spacecraft and its payload.
It also is known that bi-metallic elements, such as those used in thermostatic controls and the like, may cause movement within a latch or release mechanism. Such thermostatically actuated release mechanisms may be used to actuate various types of fire protection equipment in response to an increase in heat in the vicinity of the bi-metallic element. However, such conventional actuating and releasing devices employing bi-metals have the disadvantage of generating only low levels of movement force. Accordingly, bi-metallic elements generally are not capable of generating the high levels of tension needed to withdraw a heavy metal shaft from binding engagement with separable pieces of a spacecraft. Even highly tensioned springs as may be used in conventional bolt cutter assemblies sometimes fail to overcome the level of binding friction occurring between two separable pieces held together by the shaft of a launch lock.